1. Field of the Invention
The present invention relates generally to a mechanical seal device with an enhanced seal performance and durability used for pumps or the like. More particularly, the invention relates to a mechanical seal device which provides a seal against a process fluid under a high pressure and exhibits an improved durability of seal rings.
2. Description of the Related Art
There has been a mechanical seal device as a relative art of the present invention, as shown in FIG. 6.
FIG. 6 shows a half sectional view of the mechanical seal device 100 being used for a pump.
In this mechanical seal device 100, an apparatus interior side F defines a sealed process fluid region dealing with water or the like while an external side T which is opposite to the apparatus interior side F defines a region of lubricant oil or atmosphere.
This mechanical seal 100 is disposed between a housing 102 and a rotary shaft 103. A rotary body 104 which is connected with the rotary shaft 103 retains a step shoulder 104A. The step shoulder 104A is disposed at the end portion 104C within an inner circumferential surface 104B of the rotary body 104. The inner diameter surface 104B needs to be made large in diameter. Therefore, it is difficult to enforce a large width for a radially extending surface 104D of the step shoulder 104A. A rotary seal ring 106 is installed within the step shoulder 104A via a cup gasket 105. The inner diameter surface 105A of the cup gasket 105 is made smaller than the inner circumferential surface 104B of the rotary body 104 according to the size of the rotary seal ring 106.
A stationary seal ring 107 which is disposed opposite to the rotary seal ring 106 and forms a sealing contact therewith is fitted to a casing 108 in a movable manner. The casing 108 then is fitted to a housing 102. And the stationary seal ring 107 is resiliently urged toward the rotary seal ring 106 by a spring 111. The spring 111 disposes annular spring seats 110, 110 on its both ends whose cross section is L-shaped. Furthermore, the spring seats 110, 110 are disposed between the two end flanges of a flexible diaphragm 109 which has a cylindrical shape and whose middle portion is bent for providing flexibility.
The mechanical seal device 100 thus formed provides a seal against a process fluid by establishing a sealing contact between the cup gasket 105 and the contact surface of the step shoulder 104A even under a process fluid pressure exerted from the direction of the apparatus body side F. Moreover, the cup gasket 105 resiliently supports the rotary seal ring 106 and urges a sealing contact for the seal face 106A of the rotary seal ring 106.
The cup gasket 105, however, is squeezed between the hardened rotary seal ring 106 and rotary body 104 due to the process fluid pressure, and this will lead to a formation of fracture plane 105X as shown in FIG. 7. This kind of damage to the cup gasket 105 will result in an unstable behavior of the mating surface. This will yield not only an immature contact of the seal face 106A but also leakage of the process fluid.
The cup gasket even being made of a high strength rubber material is constantly subjected to a high pressure via the rotary seal ring 106 and will end up with a failure due to its decreased durability.
There exists another prior art in which the cup gasket 105 is replaced by an O-ring. However, use of O-ring is problematic in terms of its seal performance at the respective interfaces of the O-ring with the rotary seal ring 106 and the rotary body 104. That is, with such an O-ring installed, the rotary seal ring 106 is directly fitted to the step shoulder of the rotary body 104 without a resilient support. Therefore, a seal performance of a seal face 106A of the rotary seal ring 106 will deteriorate when the seal face 106A with the rotary body 104 becomes eccentric as they rotate together. Furthermore, eccentricity of the rotary seal ring 106 which is fitted to the rotary body 104 but is not resiliently supported is prone to eccentricity of the seal face 106A, which in turn induces an uneven wear of the seal face 106A and a decrease of its seal performance.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to provide a mechanical seal in which durability of a cup gasket supporting seal rings is enhanced.
Another goal is to improve a seal performance of the seal face of the seal ring by means of a support given by a cup gasket. Yet another goal is to simplify the installation of the cup gasket and the seal rings.